As a result of wear, the disc brake rotors of automobiles and the like wear unevenly and develop grooves therein. To extend their life, the rotors are machined in a lathe. The lathe removes the irregular outer surface of metal such that the rotor, after machining, is smooth. It is desirable to machine such disc brake rotors without removing them from a vehicle, with a portable external rotor and lathe assembly such as shown in U.S. Pat. No. 4,854,199 which has been assigned to the assignee of the present application. Another such portable brake lathe is shown in U.S. Pat. No. 4,388,846. The machining of the disc brake rotor while it remains on the vehicle requires less operating space than is needed for a conventional stand alone lathe that machines brake rotors after their removal from a vehicle. Furthermore, some wheel rotors cannot be removed without destroying the wheel bearings, and time is consumed in removing and reinstalling the discs on the vehicle, all of which results in higher costs. To machine the brake discs while on the vehicle, an exterior drive assembly is required which will rotate a wheel hub at a constant speed during the machining operation. Such external drive assemblies, however, are not affixed to the automobile, but are positioned adjacent the wheel hub. As as result, the drive assembly and the wheel hub may not be perfectly aligned with each other. If the connection between the two is not adapted to account for some misalignment, the drive assembly may fail and damage may be caused to the wheel hub. The present invention is intended to provide a drive assembly which has sufficient flexibility designed therein so as to enable it to operate efficiently, even when the drive assembly is not perfectly aligned with the wheel hub.